1. Field of the Invention
This invention relates to a control system for internal combustion engines, and more particularly to a control system which controls the fuel injection amount and the ignition timing in response to the flow rate of exhaust gases to be recirculated through an exhaust gas recirculation passage provided in the engine.
2. Prior Art
Conventionally, internal combustion engines are well known, which are provided with an exhaust gas recirculation passage for recirculating part of exhaust gases emitted from the engine to the intake system thereof, and an exhaust gas recirculation control valve for controlling the flow rate of exhaust gases to be recirculated through the exhaust gas recirculation passage, to thereby reduce NOx present in exhaust gases emitted from the engine. Further, there are known control systems for internal combustion engines of this type, for example, from Japanese Provisional Patent Publication (Kokai) No. 64-53032, which estimate the amount of exhaust gases to be recirculated and the amount of air to be drawn into the engine, from operating conditions of the engine, to thereby calculate the fuel injection amount, based on the estimated amounts.
However, the above prior art does not contemplate a so-called "dynamic delay" of exhaust gases to be recirculated to the engine, which is a time lag from the time the amount of exhaust gases to be recirculated is calculated to the time the calculated amount of exhaust gases is actually supplied to the engine. In particular, immediately after a change in the air-fuel ratio of an air-fuel mixture supplied to the engine from a rich state to a lean state or vice versa, the amount of exhaust gases to be recirculated through the exhaust gas recirculation passage cannot be accurately calculated, resulting in that air-fuel ratio control, fuel injection amount control, further ignition timing control, etc. cannot be carried out with high accuracy. In other words, according to the prior art, since no contemplation is made of the dynamic delay of exhaust gases to be recirculated, the degree of convergency of the air-fuel ratio to a desired valve is degraded immediately after a shift of the air-fuel ratio from a lean state to a rich state or vice versa, leading to degraded exhaust emission characteristics, or incapability of optimal control of the ignition timing, and hence degraded driveability of the engine.